SelectFormat Class Reference

Detailed Description

SelectFormat supports the creation of internationalized messages by selecting phrases based on keywords. The pattern specifies how to map keywords to phrases and provides a default phrase. The object provided to the format method is a string that's matched against the keywords. If there is a match, the corresponding phrase is selected; otherwise, the default phrase is used.

The main use case for the select format is gender based inflection. When names or nouns are inserted into sentences, their gender can affect pronouns, verb forms, articles, and adjectives. Special care needs to be taken for the case where the gender cannot be determined. The impact varies between languages:

English has three genders, and unknown gender is handled as a special
case. Names use the gender of the named person (if known), nouns referring
to people use natural gender, and inanimate objects are usually neutral.
The gender only affects pronouns: "he", "she", "it", "they".

German differs from English in that the gender of nouns is rather
arbitrary, even for nouns referring to people ("Mädchen", girl, is neutral).
The gender affects pronouns ("er", "sie", "es"), articles ("der", "die",
"das"), and adjective forms ("guter Mann", "gute Frau", "gutes Mädchen").

French has only two genders; as in German the gender of nouns
is rather arbitrary - for sun and moon, the genders
are the opposite of those in German. The gender affects
pronouns ("il", "elle"), articles ("le", "la"),
adjective forms ("bon", "bonne"), and sometimes
verb forms ("allé", "allée").

Some other languages have noun classes that are not related to gender, but similar in grammatical use. Some African languages have around 20 noun classes.

To enable localizers to create sentence patterns that take their language's gender dependencies into consideration, software has to provide information about the gender associated with a noun or name to MessageFormat. Two main cases can be distinguished:

For people, natural gender information should be maintained for each person. The keywords "male", "female", "mixed" (for groups of people) and "unknown" are used.

For nouns, grammatical gender information should be maintained for each noun and per language, e.g., in resource bundles. The keywords "masculine", "feminine", and "neuter" are commonly used, but some languages may require other keywords.

The resulting keyword is provided to MessageFormat as a parameter separate from the name or noun it's associated with. For example, to generate a message such as "Jean went to Paris", three separate arguments would be provided: The name of the person as argument 0, the gender of the person as argument 1, and the name of the city as argument 2. The sentence pattern for English, where the gender of the person has no impact on this simple sentence, would not refer to argument 1 at all:

{0} went to {2}.

The sentence pattern for French, where the gender of the person affects the form of the participle, uses a select format based on argument 1:

{0} est {1, select, female {allée} other {allé}} à {2}.

Patterns can be nested, so that it's possible to handle interactions of number and gender where necessary. For example, if the above sentence should allow for the names of several people to be inserted, the following sentence pattern can be used (with argument 0 the list of people's names, argument 1 the number of people, argument 2 their combined gender, and argument 3 the city name):

Patterns and Their Interpretation

The SelectFormat pattern text defines the phrase output for each user-defined keyword. The pattern is a sequence of keyword{phrase} clauses. Each clause assigns the phrase phrase to the user-defined keyword.

Keywords must match the pattern [a-zA-Z][a-zA-Z0-9_-]*; keywords that don't match this pattern result in the error code U_ILLEGAL_CHARACTER. You always have to define a phrase for the default keyword other; this phrase is returned when the keyword provided to the format method matches no other keyword. If a pattern does not provide a phrase for other, the method it's provided to returns the error U_DEFAULT_KEYWORD_MISSING. If a pattern provides more than one phrase for the same keyword, the error U_DUPLICATE_KEYWORD is returned.
Spaces between keyword and {phrase} will be ignored; spaces within {phrase} will be preserved.

The phrase for a particular select case may contain other message format patterns. SelectFormat preserves these so that you can use the strings produced by SelectFormat with other formatters. If you are using SelectFormat inside a MessageFormat pattern, MessageFormat will automatically evaluate the resulting format pattern. Thus, curly braces ({, }) are only allowed in phrases to define a nested format pattern.